1. Field of the Invention
This invention relates to processes for preparing 1-dichloroalkanoyl-4-(substituted phenoxy)benzenes and to processes for preparing certain intermediates therefor.
2. The Prior Art
U.S. Pat. No. 3,966,826 discloses the preparation of 1-hydroxy-4-(2-chloro-4-trifluoromethylphenoxy)benzene via the reaction of the potassium salt of hydroquinone with 3,4-dichlorobenzotrifluoride (i.e., 1,2-dichloro-4-trifluoromethylbenzene) followed by acid hydrolysis. Patentee also teaches that the addition reaction is conducted at 120.degree. to 200.degree. C. in the presence or absence of a copper catalyst. U.S. Pat. No. 4,031,131 discloses the preparation of 1-carboxy-3-(2-chloro-4-trifluoromethylphenoxy)benzene and esters thereof by reacting a disalt of 3-hydroxybenzoic acid with 1,2-dichloro-4-trifluoromethylbenzene in a polar aprotic organic solvent such as dimethylsulfoxide, dimethylformamide, sulfolane, N-methyl-2-pyrrolidone, hexamethylphosphoric triamide, etc. Chemical Abstracts discloses that Japanese Pat. No. 75:58,228 discloses the preparation of 1-acetyl-4-(2-chloro-4-trifluoromethylphenoxy)benzene.
It is also known that diaryl ethers can be synthesized by an Ullmann coupling of aryl halides with metal phenolates; e.g. see The Merck Index--Ninth Edition, p. ONR-89, Merck & Co., Inc. (1976). The preparation of dichloroacetophenone via the chlorination of acetophenone in glacial acetic acid is described in Organic Synthesis Vol. 3, p. 538 (1955).
U.S. patent application Ser. No. 126,254, filed on even date herewith by John W. Kobzina, discloses certain novel 1-dichloroalkanoyl(substituted phenoxy)benzenes, which are useful as mite ovacides, which disclosure is hereby incorporated by reference. Such compounds include 1-dichloroacetyl-4-(2-chloro-4-trifluoromethylphenoxy)benzene and 1-dichloroacetyl-4-(2-trifluoromethyl-4-chlorophenoxy)benzene.
One of the problems associated with the preparation of these compounds is the separation of the compounds from isomers and other unidentified impurities formed in the reaction product. Such impurities are formed during the preparation of the product and also during the preparation of the intermediates therefor. The separation of such impurities from the products and intermediates is very difficult on a large scale basis because, among other problems, of the solubility of both the products, intermediates and impurities in commercial solvents, such as hexane, etc. Thus, while the products and intermediates can be separated by sophisticated laboratory techniques, such as high pressure liquid chromatography, such techniques are not commercially practical for large scale production.